Turnbull, A; Crocker, L E (2014) Four point bend testing - finite element analysis of the stress and strain distribution accounting for lateral specimen curvature. NPL Report. MAT 66

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Abstract

Finite element (FE) computations of the stress and strain distribution on the tensile surface of a four point bend specimen of a 13Cr stainless steel (SS) has been carried out previously for flat specimens. However, four point bend specimens prepared from pipeline material with the weld root intact are inherently curved, with the extent of that curvature dependent on the inner diameter of the pipe. To assess the potential impact of that curvature on test methodology and test results, supplementary FE computations were carried out on specimens from a pipe with a relatively small inner diameter of 12.1 cm with specimen widths of 20 mm and 12 mm. The results indicated that for elastic loading the stress and strain tended to increase towards the specimen edges (i.e. thicker section of the specimen). Above yield, the total strain and the plastic strain were higher towards the edges but stress relaxation and redistribution following yielding resulted in a very small variation in stress across the specimen, with a maximum away from the edges. To limit the potential effect of curvature, it is recommended that the width of the specimen be minimised for small diameter pipe, with a width of specimen thickness ratio not greater than 1.5 times the thickness.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MAT 66
Keywords:	finite element, four point bend
Subjects:	Advanced Materials Advanced Materials > Corrosion
Last Modified:	02 Feb 2018 13:13
URI:	http://eprintspublications.npl.co.uk/id/eprint/6197

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